The primary objective of the current research program is to define and characterize the molecular basis for innate resistance and susceptibility of inbred strains of the snail Biomphalaria glabrata to infection by larvae of the human blood fluke Schistosoma mansoni, causative agent of hepatosplenic schistosomiasis. Information gained over the last grant period strengthens a critical, but complex, nexus between larval- expressed carbohydrates (CHOs) and hemocyte immune function. As a result, the current research plan will take an integrated cellular, biochemical and molecular approach to evaluate the role of hemocyte pattern recognition receptors, emphasizing CHO-reactive lectins, in immune recognition of and reactivity to schistosome-specific CHOs. The central hypothesis to be addressed is that parasite CHOs represent the primary pathogen-associated molecular patterns (PAMPs) responsible for hemocyte immune recognition, but differential responses by susceptible (S) and resistant (R) snail cells (e.g., CHO-reactivity, larval adherence, oxidative responses) are due either to differences in CHO-recognizing receptors, receptor repertoires, signaling pathways required for effector activity, or relative sensitivities to anti-immune parasite mechanisms. To address this hypothesis, research efforts will be directed towards (1) characterizing structural and functional properties of known hemocyte lectin-like receptors, while attempting to discover new ones, (2) determining if schistosome-specific CHOs serve as ligands for lectin-like receptors, and if so, whether they are capable of eliciting or inhibiting hemocyte encapsulation responses or generation of reactive oxygen species (ROS), (3) critically evaluating the role of protein kinase C, mitogen-activated protein kinases (Erks, p38) and a Rac-like GTPase in signaling immune effector responses, particularly induction of respiratory burst activity (H2O2 production), in S and R snail hemocytes upon specific CHO stimulation, and (4) explore the role of exogenous H2O2 as a signaling molecule (second messenger) in modulating hemocyte behavior or parasite antioxidant activity. It is anticipated that research findings generated as a result of this project will provide a unifying model linking together the initial hemocyte-CHO interaction, signaling events triggered by ligand-receptor binding, and terminating in expression of hemocyte effector function (ROS response). In addition to providing important insights into the role of schistosome CHOs in regulating hemocyte responses to early developing schistosomes, this work will contribute to a greater understanding of the mechanisms of innate immune recognition and pathogen anti-immune responses that may well lead to the development of novel approaches to controlling these snail vectors of human disease or the pathogens they carry. PUBLIC HEALTH RELEVANCE: The primary goal of the current project is to define and characterize the molecular basis for innate immune resistance of inbred strains of the snail Biomphalaria glabrata to infection by larvae of the human blood fluke Schistosoma mansoni, causative agent of hepatosplenic schistosomiasis. Schistosome parasites infect an estimated 200 million people in over 70 countries worldwide, severely impacting the general public health, vitality, and productivity of affected populations, especially developing nations in the tropics. Because these pathogens require snail intermediate hosts for completing their life cycle and transmission to humans, information on the mechanisms of immune reactivity in snails against larval infection will be critical in understanding the genetic basis for host resistance. Therefore, knowledge gained from the proposed studies could very well lead to the development of more effective and novel methods for controlling human schistosome transmission by disrupting parasite development within the snail host.